Plant pests are a major factor in the loss of the world's important agricultural crops. About $8 billion are lost every year in the U.S. alone due to infestations of invertbrate pests including nematodes. In addition to losses in field crops, nematode pests are also a burden to vegetable and fruit growers, to producers of ornamental flowers, and to home gardeners. Plant-infesting nematodes, a majority of which are root feeders, are found in association with most plants. Some are endoparasitic, living and feeding within the tissue of the roots, tubers, buds, seeds, etc. Others are ectoparasitic, feeding externally through plant walls. A single endoparasitic nematode can kill a plant or reduce its productivity. Endoparasitic root feeders include such economically important pests as the root-knot nematodes (Meloidogyne species), the reniform nematodes (Rotylenchulus species), the cyst nematodes (Heterodera species), and the root-lesion nematodes (Pratylenchus species). Direct feeding by nematodes can drastically decrease a plant's uptake of nutrients and water. Nematodes have the greatest impact on crop productivity when they attack the roots of seedlings immediately after seed germination. Nematode feeding also creates open wounds that provide entry to a wide variety of plant-pathogenic fungi and bacteria. These microbial infections can be more economically damaging than the direct effects of nematode feeding.
Cyst nematodes are responsible for direct loss in soybean yield and indirect loss due to cost of pesticides and non-optimal use of land for rotation. Soybean cyst nematode (Heterodera glycines) has a negative economic impact that may exceed $1 billion per year in North America. Economically significant densities of cyst nematodes usually cause stunting of crop plants. The stunted plants have smaller root systems, show symptoms of mineral deficiencies in their leaves, and wilt easily.
Traditional practices for managing nematode infestations include maintaining proper fertility and soil pH levels in nematode-infested land; controlling plant diseases that aid nematode invasion, as well as controlling insect and weed pests; using sanitation practices such as plowing, planting, and cultivating of nematode-infested fields only after working non-infested fields; cleaning equipment thoroughly after working in infested fields; not using seed from plants grown on infested land for planting non-infested fields unless the seed has been properly cleaned; rotating infested fields and alternating host crops with non-host crops, such as, corn, oat and alfalfa and planting resistant or tolerant plant varieties. While many of these can be effective they are time consuming and costly to implement. Nematodes are difficult pests to control without the use of chemical pesticides or fumigants (e.g., nematicides), and the availability of these nematicides is decreasing due to high toxicity to humans and the environment. Furthermore, under the Montreal Protocol of 1987, one of the main chemicals used to control nematode infestation, methyl bromide, has been phased out. Thus, there is currently no efficient and effective approach to control nematode infestation of plants.
Biological pest control agents, such as Bacillus thuringiensis strains expressing pesticidal toxins like delta-endotoxins (also called Cry proteins), have been applied to crop plants with satisfactory results, offering an alternative or compliment to chemical pesticides. Some Cry proteins, for example Cry1, Cry 5, Cry6, Cry11, Cry12, Cry13, Cry14, Cry21 and Cry22, have been shown to provide some activity against certain nematode species in laboratory bioassays. However, control of nematode pests by expression of Cry proteins in plants has not been demonstrated, particularly in field crops such as soybean or corn.
Other, non-endotoxin genes and the insecticidal proteins they encode have also been identified. U.S. Pat. Nos. 5,877,012, 6,107,279, 6,137,033, and 6,291,156, as well as Estruch et al. (1996, Proc. Natl. Acad. Sci. 93:5389-5394) and Yu et al. (1997, Appl. Environ. Microbiol. 63:532-536), describe a new class of insecticidal proteins called. Vip3 (vegetative insecticidal protein 3). Vip3 genes encode approximately 88 kDa proteins that are produced and secreted by Bacillus during its vegetative stage of growth (vegetative insecticidal proteins, VIP). For example, one family of the Vip3 protein class, called Vip3A, possesses insecticidal activity against a wide spectrum of lepidopteran pests, including, but not limited to, black cutworm (BCW, Agrotis ipsilon), fall armyworm (FAW, Spodoptera frugiperda), tobacco budworm (TBW, Heliothis virescens), and corn earworm (CEW, Helicoverpa zea). More recently, plants expressing the Vip3A protein have been found to be resistant to feeding damage caused by hemipteran insect pests (U.S. Pat. No. 6,429,360). Thus, Vip3A proteins display a unique spectrum of insecticidal activities. Other disclosures, WO 98/18932, WO 98/33991, WO 98/00546, and WO 99/57282, have also now identified homologues of the Vip3 class of proteins. Proteins from the Vip3 class have heretofore not been shown to have any activity against non-insect pests such as nematodes.
Due to the above described limitations in the art, there remains a need to develop new methods for controlling nematode plant pests that provide an economic benefit to farmers and that are environmentally acceptable.